This invention relates to a subscriber line test system to be carried out for maintenance of a subscriber line connecting a customer station equipment and an exchange.
In a conventional subscriber line test system, to detect disconnection, earth fault and contact with electric wire in a subscriber line, at first a subscriber line to be tested is selected on a line test table of exchange, next, analog parameters such as insulation resistance and capacity between subscriber lines and voltage to ground are measured.
A digital subscriber line test system, which is shown in Japanese Patent Laid-Open No. 77460/1986, is proposed to test in a digital subscriber line transmission system using installed metallic cable in such steps of providing a relay and a terminating resistor for matching, operating said relay with a line terminating device in said end terminal by receiving a demanding signal for testing from an office, cutting off said digital subscriber line in a fixed time from the line terminating device in said terminal side, mutually releasing said digital subscriber lines or terminating by using said terminating resistor for matching, and in this time, testing said digital subscriber line with a subscriber line test device installed in said office.
This conventional subscriber line test system, however, has problems as below. For example, it is impossible to start a test from a customer station equipment at working for the customer station device, because selection of the subscriber line to be tested is done on the side of the exchange, more it is impossible to determine which side of a subscriber line or a subscriber circuit has fault points. Also testing items are matched to a transmission system of a conventional analog type, it is difficult to evaluate the problems such as instantaneous cut of the subscriber line, deterioration of transmission quality by interference of noise, or the like that are especially serious at digital transmission.
Further, another digital subscriber line test system, which is shown in Japanese Patent Laid-Open No. 239729/1986, is proposed. The proposed system is comprised of a signal processing section and a line interface section, wherein said signal processing section has a transmission channel for control signals and a reception channel of control signals between a line terminating section through said line interface section, and in a digital terminal device wherein said line interface section has a channel for echo control signals receiving echo control signals sent back from said line terminating section, when said line interface section receives a test mode signal from said signal processing section, it transmits an echo control signal transmitted from said line terminating section through the channel for said echo control signal, to said signal processing section through the channel for said control signal.
However, even using the proposed arts, only a few subscriber lines can be measured when testing subscriber lines. So that this art is also in dissatisfaction.